1. Field of the Invention
The present invention relates to a display having a plurality of organic electroluminescence (EL) devices in which a first electrode, at least one organic layer including a luminescent layer, and a second electrode are sequentially stacked, and getting light generated in the luminescent layer out of the second electrode side, and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, a display using a self-emitting device such as a light emitting diode (LED), a laser diode (LD), or an organic electroluminescence device has been being developed. In the display of this kind, generally, a screen (display panel) is constructed by disposing a plurality of self-emitting devices in a matrix and each of the devices is selectively allowed to emit light in accordance with a picture signal, thereby displaying an image.
A display using the self-emitting devices has advantages such that a backlight required in a display of a non self-emitting type such as a liquid crystal display (LCD) is unnecessary. Particularly, in recent years, attention is paid to a display using organic EL devices (organic EL display) for the reasons such as wide angle of visibility, high visibility, and high speed of response of the devices.
An EL device has, for example, a structure in which a first electrode, organic layers including a luminescent layer, and a second electrode are sequentially stacked on a substrate for driving. In such an organic EL device, depending on the type of a display, light generated in the luminescent layer may emit from the substrate for driving or the second electrode side.
A display using such organic EL devices has a problem such that external light reflection by the organic EL devices and a wiring electrode between the devices is large and the contrast of the display deteriorates. In order to deal with the problem, a method of preventing the external light reflection by disposing a color filter or a black matrix has been proposed. For example, as a display of a type in which light is emitted from the second electrode side, the applicant herein has proposed a display in which an absorption filter of G (green) is disposed on the light output side of each of pixels of R (red) and B (blue) or on the external light incident side (Japanese Patent Application No. 2001-181821). In the proposal, considering that the naked eye has high sensitivity to light in the range of wavelength of G, the absorption filter of G is disposed for each of pixels of R and B to absorb the G component of incident external light and transmit light of R and B, thereby realizing dramatic improvement in contrast without deteriorating the brightness of an inherent luminescent color.
The configuration of using the color filter as in the proposal mainly aims at reducing external light reflection by the organic EL device itself. On the other hand, to suppress external light reflection by wiring electrodes and the like provided around pixels, a black matrix is used. Conventionally, as a black matrix of an organic EL display, in a manner similar to a liquid crystal display, for example, a thin film filter obtained by laminating thin films made of chrome (Cr) and chromium oxide and patterning the resultant by lithography technique and etching or a black resin film obtained by exposing a photosensitive resin with light and patterning the resin is used.
However, the role of the black matrix in an organic EL display and that in a liquid crystal display are quite different from each other, and required shape precision and optical density of an organic EL display and those of a liquid crystal display are also largely different from each other. Specifically, in a liquid crystal display, the black matrix has functions of defining the aperture ratio of pixels and shielding a backlight, so that high shape precision is required and optical density of 3 is necessary. In contrast, since no backlight is provided for an organic EL display, the optical density of 2 of the black matrix is sufficient, and high precision of the shape and position is not so required. The aperture ratio of pixels is defined by an insulating film made of silicon dioxide (SiO2) or the like for electrically insulating first and second electrodes from each other, and has no relation with the black matrix. Therefore, the main object of disposing a black matrix in an organic EL display is to prevent external light reflection by a wiring electrode provided between devices. Forming a black matrix equivalent to that in a liquid crystal display in an organic EL display causes unnecessary increase in cost.
Requirements for a color filter in a liquid crystal display and those in an organic EL display are also different from each other. In a liquid crystal display, high-precision alignment is required so that backlight does not leak from a gap between color filters, and the surface of the color filter is preferably flat to sandwich liquid crystal. The cheapest method of forming a color filter is printing. In the printing, however, the edges of a pattern tend to be rounded and there is the possibility the aperture ratio decreases or varies in a liquid crystal display. For such reasons, the lithography technique is more widely used than printing for a liquid crystal display. However, in an organic EL display, the necessity of performing such a high-precision color filter fabricating process is low. Further, the material itself of a color filter is expensive and its cost makes up a considerable part of a liquid crystal display. In order to commercialize an organic EL display in full gear, it is indispensable to reduce the cost of the color filter and fabrication of the color filter.
Various attempts have been being made to replace the black matrix with a multilayer color filter of two or more colors in order to reduce cost. Reported examples include a technique of stacking color filters of single color or two or more colors in a frame portion of a substrate, and using the resultant as a shield layer (Japanese Patent Laid-Open Nos. 10-62768 and 2000-29014) and a technique of providing a multilayer color filter part between picture elements so as to also serve as a part of a black matrix or a partition for making liquid crystal molecules orient in an axially symmetrical fashion (Japanese Patent Laid-Open No. 2000-89215).
Another example is a multilayer color filter which can be used for not only a liquid crystal display but also various displays, color sensors, and the like, in which two layers of a resin of the same color are stacked in a pixel portion and resins of different two colors are stacked in a light shielding portion surrounding the pixel portion (Japanese Patent Laid-Open No. 2-287303). However, it has been pointed out that the configuration has a narrow alignment margin and it is difficult to apply the invention at least to a liquid crystal display (Japanese Patent Laid-Open Nos. 2000-29014 and 2000-89215). Since two layers of resin of the same color are stacked in the pixel portion, patterning by lithography has to be performed total six times in order to form two pattern layers of color filters of three colors, and the like, the manufacturing processes are too complicated from the viewpoints of performance and characteristics required for the color filters of an organic EL display, and an effect at reducing the cost which is the most important subject right now is poor.